Possible warnings (3)

kernel/printk/printk.c:186:16: warning: 'old' may be used uninitialized in this function [-Wuninitialized]
arch/x86/kernel/apic/io_apic.c:1033:6: warning: 'irq' may be used uninitialized in this function [-Wuninitialized]
arch/x86/kernel/e820.c:651:16: warning: 'gapstart' may be used uninitialized in this function [-Wuninitialized]